Welding transformer control system



Feb. 6, 1951 H. W. SNYDER WELDING TRANSFORMER CONTROL SYSTEM Filed March29, 1946 NVENTGR 5A a may ilp 3 a:,

1 ATTOR N EY Patented Feb. 6, 1951 WELDING TRANSFORMER CONTROL SYSTEMHenry W. Snyder, West Allis, Wia, assignor to Allis-ChalmersManufacturing Company, Milwaukee,

Wis., a corporation of Delaware Application March 29, 1946, Serial No.658,048

1 6 Claims.

This invention relates in general to improvements in control systems forwelding transformers, and more particularly to means for reducing thevoltage of a welding transformer while the transformer is not carryingload cur rent.

The supphr of alternating current to welding electrodes is frequentlyeffected through a transformer having a secondary open circuit voltageof such magnitude as to constitute, under favorable circumstances, asubstantial hazard to a human being touching both electrodessimultaneously. It is therefore desirable to energize the transformer atreduced voltage while the transformer is not carrying load current.

Control systems for performing the latter function generally compriseswitching devices such as contactors and relays which are provided withoperating coils. To insure that the welding transformer is notaccidentally energized at full voltage in response to burning out of anoperating coil, the system should be so designed that such energizationtakes place only in response to energization of the operating coils atsuflicient voltage to cause operation of the switching devices of whichthey are a part. The impedance of an operating coil increasing severalfold upon operation of the associated armature, there is also a dangerthat a coil may burn out if it is energized for a substantial length oftime at a voltage insufllclent to cause operation of the switchingdevice of which it is a part.

' For the reasons above set forth, it is advantangeous to provide asystem of the character herein considered with switching devices whosecoils are substantially entirely deenergized while the weldingtransformer is idle. In a preferred embodiment of the invention the coilof the. device initiating the impression of full voltage on the weldingtransformer is connected across impedance means such as an inductivereactor joining the welding transformer secondary, winding to thewelding circuit so that the coil is at least substantially entirelydeenergized when the welding circuit is without current.

It is therefore an object of the present invention to provide animproved system for reducing the open circuit voltage of a weldingtransformer in which the coils of all switching devices are deenergizedwhile the transformer is idle.

Another object of the present invention is to provide an improved systemfor reducing the open circuit voltage of a welding transformer in whichburning out of an actuating coil of a switching device will preventenergization of the welding transformer at full voltage.

Objects and advantages other than those above set forth will be apparentfrom a consideration of the following description when read inconnection with the accompanying drawing which diagrammaticallyillustrates one embodiment of the present invention applied to thecontrol of a welding transformer adapted to be energized at voltages ofdifferent values.

Referring more particularly to the drawing by characters of reference,numeral 6 designates a welding transformer provided with a primarywinding 6a and with parallel secondary windings 6b, 6c. The secondarywindings are connected with a welding circuit 1 for supplying current toa pair of electrodes 8, 9 of which electrode 8 is assumed to be a rod ofweld metal and electrode 9 the work to be welded. The flow of currentthrough electrodes 8, 9 is adjustably limited by suitable impedancemeans, such as an adjustable reactor ll of any suitable type. Thereactor core may be distinct from the core of transformer 6, or the twocores may comprise a common portion. In the latter instance the reactorwinding and windings 6a, 6b, 6c may be inductively related to a limitedextent.

Winding 6a is provided with a plurality of pairs of terminals which maybe selectively connected with a source of alternating current, such as acircuit l2 energized from a suitable generator (not shown) throughconnections which may include disconnecting switches I3 and the maincontacts b of a contactor switch I, to cause energization of circuit 1at the normal operating voltage thereof.

Circuit 1 may also be energized at a voltage lower than the normal opencircuit voltage of winding 6b, by means of an auxiliary transformer is.The primary winding lid of transformer is may be energized from circuitl2 and is therefore provided with different voltage taps to permitenergization thereof at different voltages without changing the value ofthe voltage induced in the associated secondary winding l5b. The latterwinding is provided with terminals I50, l5d and with a tap l5e. One ofthe conductors of circuit 1 is connected with tap lie through a lowresistance connection and the other conductor of circuit 1 is connectedwith one of terminals of windings l5b through reactor II and contactslllc of switch I4.

Operating coil Ila of switch It may be ener-v gized from any suitablesource and is conveniently connected between terminals |5c, 15d throughcontacts 16b of a relay IS. The coil lid of relay It is connected acrossreactor ll through contacts llc, lld to cause relay It to close contactslib in to the now of current through reactor II. The speed of operationof relay It may be established at any desired value by proper choice ofthe relay elements, which may include any suitable known delaying meansconventionally represented as a dashpot lic. Suitable impedancemeanssuch as a resistor ll may be inserted in series with coil its byopening of contacts lic, lid to limit the heating of coil lie when thecoil is energized In operation, circuit I! being energised and switchesll being closed, transformer Ii is energized from circuit II but windingis remains operatively disconnected from circuit I! as long as contactslib are open. A reduced voltage depending upon the choice of tap lie isthen impressed from winding lib on the circuit extend ing from tap liethrough one of the conductors of circuit I, windings 6b, ic and contactslie to terminal lic. Tap lie is so chosen that the voltage thusimpressed on circuit 1 and electrodes I, i is of such low value as notto constitute a substantial hazard to human life. No load current flowsthrough reactor II .and coil lia remains deenergized as long aselectrodes i, 9 are not brought into engagement, except for a negligibleamount of current which may be supplied to coil lia from reactor II as aresult of any inductive relation between the reactor winding and thewindings of transformer i. Coil lid is then entirely deenergized.

Welding operation may be initiated by bringing electrode i in contactwith electrode 0.

Winding lib then supplies a substantial current to circuit 1 throughcontacts llc and reactor II. The voltage drop in reactor II is impressedon coil lid to cause switch Ii to close contacts lib. Coil a is therebyconnectedacross terminals lic, lid, and switch ll opens contacts lic,lid and closes contacts lib. Opening of contacts lic disconnects circuit1 from winding lib. Closing 'of contacts lib causes windingia to beenergized at the full voltage of circuit l2, whereby normal operatingvoltage is induced in windings ib, Sc and is impressed on circuit 1through reactor ll.

Electrodes i, i may then be separated to draw a welding arctherebetween. Welding operation at normal voltage causes the voltagedrop in reactor II to be increased beyond the value thereoi resultingfrom energization of circuit I from winding lib and short circuiting ofelectrodes 8, i. Opening of contacts llc, lid causes resistor l! to beinserted in series with coil lid to adjust the current of the coilwithin the proper range of value for maintaining contact lib closedwithout danger of overheating coil Iia.

when the flow of current through circuit I is interrupted by separationof electrodes i, i beyond a predetermined distance, the voltage ofcircuit 1 abruptly increases to a value which may be consideredtoconstitute a hazard to human life. The voltage of. reactor ll drops-tozero or,

' at least, to a negligible value. thereby causins relay ii to opencontacts lib after a predetermined time delay. Coil its is entirelydeenergized and switch it returns to the position shown to disconnectwinding is from circuit l2 and resuited. switch it must remain in theopen osition shown or return to such position, so that accidentalenergimtion of circuit 1 while thecircuit does not carry load currentcannot take place.

Although but one embodiment of the present invention has beenillustrated and described, it will be apparent to one skilled in theartj'that various changes and modifications may be made therein withoutdeparting from the spirit of the invention or from the scope of theappended claims.

Itisclaimedanddesiredtosecurebyutters Patent: v

.1. In a control system for a welding transformercomprisingaprimarywindingtobeccnq nected to a source of alternatingcurrent and a secondary winding having a normal open circuit voltage ofdangerously high value connected to a welding circuit through impedancemeans, the combination of a switch for connecting said primary windingwith said source, transformer mealmv connecting said secondary windingwith said source for impressing on said secondary winding a voltage ofsate value below the said normal open circuit voltage thereof, and meansresponsive to the voltage drop in said impedance means operable uponshort circuiting of said welding circuit for disconnecting saidsecondary winding from said transformer means and caus ing closure ofsaid switch. v

2.-In a control system for a welding transformer comprising a primarywinding to be connected to a source of alternating current and asecondary winding having a normal open circuit voltage of dangerouslyhigh value connected to a welding circuit through impedancemeans, thecombination of a switch for connecting said primary winding with saidsource, transformer means connecting said secondary winding with saidsource for impressing on said secondary normal open circuit voltagethereof, and means comprising an operating coil connected across connectcircuit I with winding lib. Circuit 1 is then again energized at reducedvoltage and another welding cperation may be initiated in the mannerabove set forth by engagement of electrodes i. i.

It will be apparent that if either coil lie or winding a voltage of safevalue below the said said impedance means for disconnecting saidsecondary winding from said transformer means l and causing said switchto be closed in response to the flow of current through said impedancemeans.

3. In a control system for a welding transformer comprising a primarywinding to be connected to a source of alternating current and asecondary winding connected to a welding circuit through impedancemeans, the combination of a switch for connecting said primary windingwith said source, transformer means connecting said secondary windingwith said source for impressing on said secondary winding a voltagebelow the normal open circuit voltage thereof, an operating coilconnected across said impedance means, a second impedance means, andmeans responsive to energization of said operating coil fordisconnecting said secondary winding from said transformer means,closing said switch, and

connecting said second impedance means in series with said operatingcoil.

a 4. In a control system for a welding trans bination of a switch forconnecting said primary winding with said source, said switch beingprovided with an operating coil, an auxiliary transcoii lia burns out orotherwise becomes open cir- 15 former connected with said secondarywinding and with said source for impressing on said secondary winding avoltage below the normal open circuit voltage thereof, a relay forconnecting said operating coil with said auxiliary transformer to causeclosure of said switch, said relay comprising a second operating coil,means including contacts controlled by said switch connecting saidsecond operating coil across said reactor to cause operation of saidrelay in response to the flow of current through said welding circuit, aresistor connected across said contacts to limit the flow of currentthrough said second operating coil when said switch is closed, andfurther contacts controlled by said switch for disconnecting saidwelding circuit from said auxiliary transformer in response to closingoperation of said switch.

5. In a control system for a welding transformer comprising a primarywinding to be connected to a source of alternating current and asecondary winding having a normal open circuit voltage of dangerouslyhigh value connected to a welding circuit through an inductive reactor,the combination of a switch for connecting said primary winding withsaid source, said switch being provided with an operating coil, anauxiliary transformer having a primary winding \connected with saidsource and a secondary winding, terminals for said auxiliary transformersecondary winding, certain of said terminals being connected with saidwelding transformer secondary winding for impressing on said weldingtransformer secondary winding a voltage of safe value below the saidnormal open circuit voltage thereof, a relay for connecting said switchcoil with another of said terminals of said auxiliary transformersecondary winding for impressing on said switch coil a voltage ofgreater value than the voltage impressed on said welding transformersecondary winding to cause closure of said switch, said relay comprisingan operating coil, means controlled by said switch connecting said relaycoil across said reactor to cause operation of said relay in response tothe flow of current through said welding circuit. and contactscontrolled by said switch for disconnecting said welding transformersecondary winding from said auxiliary transformer in response to closingoperation of said switch.

6. In a control system for a welding transformer comprising a primarywinding and a secondary winding for supplying current to a weldingcircuit through an inductive reactor, the combination of a line switchoperable to cause energization of said welding circuit through saidtransformer and said reactor, said line switch being provided with anoperating coil, means for impressing through said reactor on saidcircuit a voltage below the normal open circuit voltage thereof, a relayfor energizing said switch coil to cause closure of said switch, saidrelay comprising an operating coil, means for controlling the operationof said relay including contacts controlled by said switch connectingsaid relay coil across said reactor to cause energization of said relaycoil in response to the flow of current through said reactor when saidvoltage below the normal open circuit voltage is impressed on saidwelding circuit, and further contacts controlled by said switch fordisconnecting said welding circuit from said voltage impressing means inresponse to closing operation of said switch. l

HENRY W. SNYDER.

REFERENCES crrnn The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,364,372 Kenrick Dec. 5, 19442,449,456 Croco Sept. 14, 1948 FOREIGN PATENTS Number Country Date749,634 France May 8, 1933

